package org.apache.lucene.store;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

/**
 * A memory-resident {@link IndexOutput} implementation.
 * 
 * @version $Id: RAMOutputStream.java 598693 2007-11-27 17:01:21Z mikemccand $
 */

public class RAMOutputStream extends IndexOutput {
	static final int BUFFER_SIZE = 1024;

	private RAMFile file;

	private byte[] currentBuffer;
	private int currentBufferIndex;

	private int bufferPosition;
	private long bufferStart;
	private int bufferLength;

	/** Construct an empty output buffer. */
	public RAMOutputStream() {
		this(new RAMFile());
	}

	RAMOutputStream(RAMFile f) {
		file = f;

		// make sure that we switch to the
		// first needed buffer lazily
		currentBufferIndex = -1;
		currentBuffer = null;
	}

	/** Copy the current contents of this buffer to the named output. */
	public void writeTo(IndexOutput out) throws IOException {
		flush();
		final long end = file.length;
		long pos = 0;
		int buffer = 0;
		while (pos < end) {
			int length = BUFFER_SIZE;
			long nextPos = pos + length;
			if (nextPos > end) { // at the last buffer
				length = (int) (end - pos);
			}
			out.writeBytes((byte[]) file.getBuffer(buffer++), length);
			pos = nextPos;
		}
	}

	/** Resets this to an empty buffer. */
	public void reset() {
		try {
			seek(0);
		} catch (IOException e) { // should never happen
			throw new RuntimeException(e.toString());
		}

		file.setLength(0);
	}

	public void close() throws IOException {
		flush();
	}

	public void seek(long pos) throws IOException {
		// set the file length in case we seek back
		// and flush() has not been called yet
		setFileLength();
		if (pos < bufferStart || pos >= bufferStart + bufferLength) {
			currentBufferIndex = (int) (pos / BUFFER_SIZE);
			switchCurrentBuffer();
		}

		bufferPosition = (int) (pos % BUFFER_SIZE);
	}

	public long length() {
		return file.length;
	}

	public void writeByte(byte b) throws IOException {
		if (bufferPosition == bufferLength) {
			currentBufferIndex++;
			switchCurrentBuffer();
		}
		currentBuffer[bufferPosition++] = b;
	}

	public void writeBytes(byte[] b, int offset, int len) throws IOException {
		while (len > 0) {
			if (bufferPosition == bufferLength) {
				currentBufferIndex++;
				switchCurrentBuffer();
			}

			int remainInBuffer = currentBuffer.length - bufferPosition;
			int bytesToCopy = len < remainInBuffer ? len : remainInBuffer;
			System.arraycopy(b, offset, currentBuffer, bufferPosition,
					bytesToCopy);
			offset += bytesToCopy;
			len -= bytesToCopy;
			bufferPosition += bytesToCopy;
		}
	}

	private final void switchCurrentBuffer() throws IOException {
		if (currentBufferIndex == file.numBuffers()) {
			currentBuffer = file.addBuffer(BUFFER_SIZE);
		} else {
			currentBuffer = (byte[]) file.getBuffer(currentBufferIndex);
		}
		bufferPosition = 0;
		bufferStart = (long) BUFFER_SIZE * (long) currentBufferIndex;
		bufferLength = currentBuffer.length;
	}

	private void setFileLength() {
		long pointer = bufferStart + bufferPosition;
		if (pointer > file.length) {
			file.setLength(pointer);
		}
	}

	public void flush() throws IOException {
		file.setLastModified(System.currentTimeMillis());
		setFileLength();
	}

	public long getFilePointer() {
		return currentBufferIndex < 0 ? 0 : bufferStart + bufferPosition;
	}
}
